European Publication No. 478,363, published Apr. 1, 1992, describes fibrinogen receptor antagonists and procedures for preparing fibrinogen receptor antagonists which are prepared according to the procedure of the present invention. In particular, the compound: ##STR2## is prepared according to an 11-step procedure involving the formation of potentially hazardous NaH/DMF for ether formation, which required a chromatographic purification.
Singerman et al., J. Heterocyclo Chem. (1966), 3, 74, describes a procedure for preparing 4-(4-pyridinyl)-butyl chloride, which requires 6 steps. The procedure of the invention requires only one step to prepare this compound.
Solar et al., J. Org. Chem. (1966), 31, 1996, describes O-alkylation of tyrosine. Selective O-alkylation of N-sulfonylated tyrosine described in the present invention is unprecedented.